Health and disease

• Communicable and non-communicable diseases:

  • communicable diseases are transferred between individuals - through the air, from parasites or by bodily fluids
  • non-communicable diseases cannot be transferred between individuals, which may be due to genetics or lifestyle factors

  The presence of one disease can lead to increased susceptibility to other diseases.
• Pathogens: a microorganism that causes disease such as viruses, bacteria, fungi, and protists

  • cholera is a bacteria spread by contaminated water, causes diarrhoea
  • tuberculosis is a bacteria that is airborne, causes lung damage
  • chalara ash dieback is a fungi that is airborne, causes leaf loss on trees
  • malaria is a protist spread by an animal vector (mosquitoes), damages the liver
  • HIV is a virus spread by bodily fluids, destroys WBC and leads to AIDs
  • Heliobacter is a bacteria spread by oral transmission, causes stomach ulcers
  • Ebola is a virus spread by bodily fluids, causes hemorrhagic fever
• Lifecycle of a virus: requires host cells to reproduce

  • lytic pathway uses host cell machinery to replicate its DNA, which is assembled to form new virus particles, once the host cell is full of virus particles, it bursts in a process called lysis
  • lysogenic pathway uses restriction enzymes to insert its DNA into the host cell's DNA, the host cell replicates, and the viral DNA is also copied, the lytic cycle begins with the assembly of new virus particles
• Sexually transmitted infections (STIs): spread through sexual contact through bodily fluids

  • chlamydia is a bacteria that can lead to infertility
  • HIV is a virus that increases the susceptibility to other infections --> AIDs

  The spread of STIs is reduced by barrier methods of contraception (e.g condoms), abstinence and education on sex
• Plant barriers:

  • physical barriers - thick cellulose cell walls or thick waxy cuticles, layer of bark (trees), thorns
  • chemical barriers - plants produce antimicrobial chemicals (can be used in atibiotics)
• Identifying plant disease:

  • in the lab, cuttings from the diseased plant are taken
  • the virus or bacteria causing the disease is grown on a culture medium
  • the pathogen is tested and identified using a monoclonal antibody testing kit
• Human barriers:

  • physical barriers - mucus, produced by goblet cells, traps pathogens, cillia wafts mucus away, skin provides a physical barrier
  • chemical barriers - lysozymes kill bacteria as tears in our eyes, hydrochloric acid in the stomach kills bacteria
• Immune response:

  • during phagocytosis (non-specific), phagocytes bind to pathogens, engulf and kill them
  • lymphocytes detect antigens on the surface pathogens, creating complimentary antibodies, which cause pathogens to agglutinate (clump together) so that phagocytes can engulf them
  • lymphocytes also produce antitoxins to neutralise toxins released by pathogens
  • antigens trigger the production of memory lymphocytes
• Immunisation:

  • vaccinations make an individual immune to a disease
  • a vaccine contains a dead or inactivated form of the pathogen, which stimulates WBC to produce antibodies
  • vaccines prevent epidemics through herd immunity, however are not always effective
• Antibiotics:

  • can only treat bacterial infections because antibiotics inhibit cell processes in the bacteria but not the host organism
• Aseptic techniques: scientist culture microorganisms to study them

  • agar jelly and Petri dishes are sterilised using an autoclave (oven) and inoculating loops are passed through a flame
  • the inoculating loops are dipped in a solution of the microorganism and spread evenly over the agar
  • a lid is taped on to stop airborne micoorganisms from contaminating the culture, but it's not completely sealed
  • a petri dish stored upside down to prevent condensation from landing on the agar surface
  • culture incubated at 25 degrees so unharmful bacteria colonies grow
• Effects of antiseptics and antibiotics:

  • grow the bacterial culture and apply a paper disc soaked in antibiotic solution
  • calculate the effectiveness of the antibiotic by measuring the diameter of the zone of inhibition, use πr2
  • area of smaller circle / area of larger circle x100 to calculate percentage of bacteria destroyed by the antibiotic
• Developing medicine: has stages including discovery, development, preclinical and clinical testing

  • preclinical testing uses cells, tissues, and animals to ensure they are safe and effective
  • clinical testing uses healthy volunteers with a low dose to ensure there are no side effects
  • clinical testing also uses patients, who are split into two groups with one receiving the drug and one receiving a placebo - can be single-blind or double-blind to remove bias
• Monoclonal antibodies: identical antibodies produced from the same immune cell can be used for different medical uses

  • mice lymphocytes (produces desired antibodies but cannot divide)
  • they are combined with tumour cells to form a hybridoma
  • hybridoma divides to produce clones, which produce the same antibody, which are collected and used
• Uses of monoclonal antibodies:

  • pregnancy tests have two sections: mobile antibodies complementary to hCG (hormone present in the urine of pregnant women) attached to blue beads, and stationary antibodies complementary to hCG stuck down to the stick
  • locating blood clots and cancer cells - the monoclonal antibodies are modified to bind to the desired molecule, and bound to fluorescent dye can be observed
  • in the treatment of cancer monoclonal antibodies bind to the antigens, called tumour markers, on the cancer cells to stimulate the immune system attack
• Advantages and disadvantages of monoclonal antibodies:

  • they bind to unhealthy cells, can be engineered to treat conditions, mouse-human hhybrid cells reduce an immune response
  • difficult to attach to drugs, expensive, mice lymphocytes trigger an immune response in humans
• Non-communicable disease:

  • cardiovascular disease is caused by high fat intake, and an inactive lifestyle
  • lung and liver disease is caused by smoking and high alcohol intake
  • vitamin and nutritional deficiencies are common in anorexia, or obesity caused by excess food intake
• Lifestyle factors:

  • obesity can lead to cardiovascular disease and high blood pressure as lipid deposits form inside blood vessels, and type 2 diabetes, malnutrition is also common in underdeveloped countries
  • BMI = mass (kg) / height2 (m), BMI over 30 is obese
  • alcohol causes liver disease
  • smoking causes lung disease, high blood pressure and heart failure
• Cardiovascular disease:

  • life-long medication reduces cholesterol and blood pressures
  • surgical procedures help the coronary artery bypass, and metal stents widen arteries
  • excercise uses respiration for energy which burns fat, so that stored fat is used up instead